Controllable ovonic phase-change semiconductor memory device and methods of fabricating the same

ABSTRACT

An ovonic phase-change semiconductor memory device having a reduced area of contact between electrodes of chalcogenide memories, and methods of forming the same. Such memory devices are formed by forming a tip protruding from a lower surface of a lower electrode element. An insulative material is applied over the lower electrode such that an upper surface of the tip is exposed. A chalcogenide material and an upper electrode are either formed atop the tip, or the tip is etched into the insulative material and the chalcogenide material and upper electrode are deposited within the recess. This allows the memory cells to be made smaller and allows the overall power requirements for the memory cell to be minimized.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 08/724,816, filed Oct. 2, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor fabricationtechniques and, more particularly, to a method for fabricating a smallcontact area between an upper and lower electrode for use in phasechangeable ("ovonic") memory devices such as, for example, chalcogenidememory cells.

2. State of the Art

The use of electrically writeable and erasable phase change materials,i.e., materials that can be electrically switched between generallyamorphous and generally crystalline states or between differentresistive states while in crystalline form, for electronic memoryapplications is well known in the art. The use of phase change materialsis disclosed, for example, in U.S. Pat. No. 5,296,716, in the names ofOvshinsky et al. ("the Ovshinsky patent"), the disclosure of which isincorporated herein by reference. The Ovshinsky patent is believed toindicate generally the state of the art, and to contain a discussion ofthe current theory of operation of chalcogenide materials.

Generally, as disclosed in the Ovshinsky patent, such phase changematerials can be electrically switched between a first structural statewhere the material is generally amorphous and a second structural statewhere the material has a generally crystalline local order. The materialmay also be electrically switched between different detectable states oflocal order across the entire spectrum between the completely amorphousand the completely crystalline states. That is, the switching of suchmaterials is not required to take place between completely amorphous andcompletely crystalline states, but rather, the material can be switchedin incremental steps reflecting changes of local order to provide a"gray scale" represented by a multiplicity of conditions of local orderspanning the spectrum from the completely amorphous state to thecompletely crystalline state. Materials with such properties are knownas "ovonic" materials.

Chalcogenide material exhibits different electrical characteristicsdepending upon its state. For example, in its amorphous state, thematerial exhibits lower electrical conductivity than it does in itscrystalline state. The operation of chalcogenide memory cells requiresthat a region of the chalcogenide memory material, called thechalcogenide active region, be subjected to a current pulse typicallywith a current density between about 10⁵ and 10⁷ amperes/cm² to changethe crystalline state of the chalcogenide material within the activeregion contained within a small pore. This current density may beaccomplished by first creating a small opening in a dielectric materialthat is itself deposited onto a lower electrode material. A seconddielectric layer, typically of silicon nitride, is then deposited ontothe dielectric layer into the opening. The second dielectric layer istypically about 40 Angstroms thick. The chalcogenide material is thendeposited over the second dielectric layer and into the opening. Anupper electrode material is then deposited over the chalcogenidematerial. Carbon is commonly used as the electrode material, althoughother materials have also been used, for example, molybdenum andtitanium nitride. A conductive path is then provided from thechalcogenide material to the lower electrode material by forming a porein the second dielectric layer by a well-known firing process.

Firing involves passing an initial high current pulse through thestructure, such that the pulse passes through the chalcogenide materialand effecting dielectric breakdown of the second dielectric layer toprovide a conductive path via the pore created through the memory cell.However, electrically firing the thin nitride layer is not desirable fora high density (i.e., high number of memory cells) memory product due tothe high current required the large amount of testing time required forthe firing.

The active regions of the chalcogenide memory cells within the pores arebelieved to change crystalline structure in response to applied voltagepulses of a wide range of magnitudes and pulse durations. These changesin crystalline structure alter the bulk resistance of the chalcogenideactive region. The wide dynamic range of these devices, the linearity oftheir response, and lack of hysteresis provide these memory cells withmultiple bit storage capabilities.

Factors such as pore dimensions (i.e., diameter, thickness and volume),chalcogenide composition, signal pulse duration and signal pulsewaveform shape have an effect on the magnitude of the dynamic range ofresistances, the absolute endpoint resistances of the dynamic range, andthe currents required to set the memory cells at these resistances. Forexample, relatively large pore diameters, e.g., about one micron, willresult in higher programming current requirements, while relativelysmall pore diameters, e.g., about 500 Angstroms, will result in lowerprogramming current requirements. The most important factor in reducingthe required programming current is limiting the pore cross sectionalarea.

The energy input required to adjust the crystalline state of thechalcogenide active region of the memory cell is directly proportionalto the dimensions of the minimum cross-sectional dimension of the pore,e.g., smaller pore sizes result in smaller energy input requirements.Conventional chalcogenide memory cell fabrication techniques provideminimum cross-sectional pore dimension, diameter or width of the pore,that is limited by the photolithographic size limit. This results inpore sizes having minimum lateral dimensions down to approximately 0.35microns. However, further reduction in pore size is desirable to achieveimproved current density for writing to the memory cell.

SUMMARY OF THE INVENTION

The present invention includes a controllable ovonic phase-changesemiconductor memory device having a small contact area betweenelectrodes of chalcogenide memory cells of a minimum cross-sectionaldimension below that achievable with existing photolithographictechniques, which device has a reduced energy input demand to operatethe chalcogenide active region. The memory cell electrodes of the deviceare further selected to provide material properties that permit enhancedcontrol of the current passing through the chalcogenide memory cell. Asa result of the reduced chalcogenide contact area, the memory cells maybe made smaller to provide denser memory arrays, and the overall powerrequirements for the memory cells are minimized. Methods of fabricatingthe memory device of the invention are also contemplated as yet anotheraspect of the invention.

Additional advantages of the invention will be set forth in part in thedescription that follows, and in part will be obvious from thedescription, or may be learned by practice of the invention.

In accordance with one purpose of the invention, as embodied and broadlydescribed herein, the invention comprises a method of manufacturing asemiconductor device comprising the steps of providing a conductivelayer on a substrate; patterning the conductive layer to form a raisedportion of the conductive layer; providing an insulating layer on theconductive layer including the raised portion; and selectively removinga portion of the insulative layer to expose part of the raised portionof the conductive layer.

In another aspect, the present invention comprises an integrated circuitdevice comprising: a substrate having a primary surface; a conductivelayer provided on the primary surface, the conductive layer having araised portion; an insulative layer overlying the first conductive layerand exposing part of the raised portion; and a layer of programmableresistive material provided in contact with the exposed part of theraised portion of the first conductive layer, the exposed part of theraised portion being of a smaller cross-sectional area than theremaining part of the raised portion of the first conductive layer.

In still another aspect, the present invention comprises an integratedcircuit comprising: a first electrode having a first portion and asecond portion, a width of the first electrode narrowing substantiallycontinuously in a direction extending from the second portion toward thefirst portion of the first electrode; a layer of programmable resistivematerial provided in contact with the first electrode; and a secondelectrode coupled to the layer of programmable resistive material.

In yet another aspect, the present invention comprises an integratedcircuit device comprising: a substrate having a primary surface; aconductive layer provided on the primary surface, the conductive layerhaving a raised portion; an insulative layer overlying the firstconductive layer and exposing part of the raised portion; a recess inthe insulative layer above the raised portion; and a layer ofprogrammable resistive material provided in contact with the exposedpart of the raised portion in the recess.

In still another aspect, the present invention comprises an integratedcircuit comprising: a first electrode having a first portion and asecond portion, a width of the first electrode narrowing substantiallycontinuously in a direction from the second portion toward the firstportion of the first electrode; a layer of programmable resistivematerial provided in a recess formed in an insulative material over thefirst electrode, wherein the programmable resistive material layer is incontact with the first electrode; and a second electrode coupled to thelayer of programmable resistive material.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention can be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIG. 1 is a side cross-sectional view of the deposition of a layer ofpolysilicon onto a substrate of titanium nitride in accordance with apreferred embodiment of the present invention;

FIG. 2 is a side cross-sectional view of the deposition of a layer ofsilicon oxide and a layer of resist material onto the layer ofpolysilicon;

FIG. 3 is a side cross-sectional view of a contact pattern that isetched in the layer of resist material and the silicon oxide layer usingetching, masking, and photoresist stripping techniques;

FIG. 4(a) is a top plan view of a generally rectangular contact patternformed from the resist material and silicon oxide layers;

FIG. 4(b) is a top plan view of a generally circular contact patternformed from the resist material and silicon oxide layers;

FIG. 5 is a side cross-sectional view of the device after the resistmaterial layer has been stripped away using strip etching techniques;

FIG. 6 is a side cross-sectional view of a portion of the layer ofpolysilicon material not covered by the silicon oxide layer pattern thatis etched using conventional undercut isotropic etching techniques toform a frusto-conical shaped tip in the layer of polysilicon material;

FIG. 7 is a side cross-sectional view of the device after the contactpattern has been removed using conventional wet etch techniques;

FIG. 8 is a side cross-sectional view of the depositing of a layer ofinsulative material onto the layer of polysilicon material, includingthe tip, using conventional thin film deposition methods to isolate thelayer of polysilicon material, including the tip;

FIG. 9 is a side cross-sectional view of planarization of the layer ofinsulative material using a conventional chemical mechanicalplanarization (CMP) process;

FIG. 10 is a side cross-sectional view of a chalcogenide material layerthat is deposited using conventional thin film deposition methods;

FIG. 11 is a side cross-sectional view of a layer of conductive materialdeposited over the chalcogenide layer using conventional thin filmdeposition techniques;

FIG. 12 is a side cross-sectional view of the layer of chalcogenidematerial and the second layer of conductive material after they areetched back using conventional masking and etching techniques;

FIG. 13 is a side cross-sectional view of a second layer of insulativematerial that is applied using conventional thin film depositiontechniques;

FIG. 14 is a side cross-sectional view of the second layer of insulatingmaterial after it is etched back;

FIG. 15 is a side cross-sectional view of the complete chalcogenidememory cell including an upper conductive grid layer;

FIG. 16 is a side cross-sectional view, which is analogous to FIG. 9,illustrating an intermediate structure after planarization of the layerof the insulative material using a conventional CMP process;

FIG. 17 is a side cross-sectional view of an etch mask formed over theinsulative material layer;

FIG. 18 is a side cross-sectional view of a recess formed by etching aportion of the frusto-conical shaped tip;

FIG. 19 is a side cross-sectional view of a chalcogenide material layerthat is deposited using conventional thin film deposition methods;

FIG. 20 is a side cross-sectional view of a layer of conductive materialdeposited over the chalcogenide layer using conventional thin filmdeposition techniques;

FIG. 21 is a side cross-sectional view of a resulting structure afterplanarization of the conductive material;

FIG. 22 is an oblique cross-sectional view of a memory cell array of thepresent invention; and

FIG. 23 is a schematic of a computer with a CPU and interacting RAM;

FIG. 24 is a side cross-sectional view of a resulting structureutilizing an optional conductive barrier layer between the conductivematerial and the chalcogenide material;

FIG. 25 is a side cross-sectional view of the deposition of a layer ofpolysilicon onto a substrate of titanium nitride in accordance with analternate embodiment of the present invention for forming anintermediate structure;

FIG. 26 is a side cross-sectional view of the deposition of a layer ofsilicon oxide and a layer of resist material onto the layer ofpolysilicon;

FIG. 27 is a side cross-sectional view of a contact pattern that isetched in the layer of resist material and the silicon oxide layer usingetching, masking, and photoresist stripping techniques;

FIG. 28 is a side cross-sectional view of the device after the resistmaterial layer has been stripped away using strip etching techniques;

FIG. 29 is a side cross-sectional view of a portion of the layer ofpolysilicon material not covered by the silicon oxide layer pattern thatis etched using conventional undercut isotropic etching techniques toform a sharp tip in the layer of polysilicon material;

FIG. 30 is a side cross-sectional view of the device after the contactpattern has been removed using conventional wet etch techniques;

FIG. 31 is a side cross-sectional view of the depositing of a layer ofinsulative material onto the layer of polysilicon material, includingthe tip, using conventional thin film deposition methods to isolate thelayer of polysilicon material, including the tip; and

FIG. 32 is a side cross-sectional view of planarization of the layer ofinsulative material using a conventional chemical mechanicalplanarization (CMP) process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of fabricating a small area of contact between electrodes ofchalcogenide memories is presented that provides an area of contact withthe lower electrode by the upper electrode, via the chalcogenidematerial, that is smaller than that presently producible usingconventional photolithographic techniques. In particular, the preferredembodiment of the present invention provides a method of fabricatingelectrodes for chalcogenide memories in which an area of contact of thelower electrode with the upper electrode is minimized by forming a tipor protrusion extending from a surface of the lower electrode. In thismanner, the lower electrode having a minimum area of contact as small asπ×(0.05 μm)² is obtained. An insulative material is applied over thelower electrode in a manner such that an upper surface of the tip isexposed, while the surrounding surface of the lower electrode remainscovered. The chalcogenide material and upper electrode are either formedatop the tip, or the tip is etched to form a recess in the insulativematerial and the chalcogenide material and upper electrode are depositedtherein as successive layers. The present invention provides enhancedcontrol of the current passing through the resulting chalcogenidememory, and thus reduces the total current and energy input required tothe chalcogenide active region in operation. The total current passingthrough the chalcogenide active region is two milliamps (mA). Thus, thecurrent density required by the preferred embodiment is 1×10⁶ A/cm² to1×10⁷ A/cm². Furthermore, the structure of the preferred embodimentallows the memory cells to be made smaller than that in the prior artand thus facilitates the production of denser memory arrays, and allowsthe overall power requirements for memory cells to be minimized.

Reference will now be made in detail to the presently preferredembodiment of the invention, an example of which is illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or equivalentelements.

It should be understood that the illustrations in FIGS. 1-23 do notcomprise actual views of any particular semiconductor device, but merelyare idealized representations which are employed to more clearly andfully depict the process and structure of the invention than wouldotherwise be possible.

Turning to the drawings and referring to FIGS. 1 to 15, a method forfabricating a small area of contact between an upper and lower electrodefor chalcogenide memories will now be described. A layer of conductivematerial 102, preferably polysilicon, is deposited onto a substrate 100using conventional thin film deposition methods such as, for example,chemical vapor deposition (CVD), as illustrated in FIG. 1. Theconductive material layer 102 may have a substantially uniform thicknessranging from about 5000 to 7000 Angstroms, and preferably will have asubstantially uniform thickness of approximately 6500 Angstroms. Thesubstrate 100 may also comprise a conductive material such as, forexample, silicon, tin, carbon, WSi_(x), or tungsten, and preferably willcomprise silicon. The substrate 100 will further preferably comprise alower electrode grid (not shown) used for accessing an array ofchalcogenide memories.

A layer of silicon oxide 104 is deposited onto the substrate 100,preferably by CVD, and will preferably have a thickness of about 500Angstroms. A layer of resist material 106 is applied onto the siliconoxide layer 104, as illustrated in FIG. 2. The resist material layer 106will preferably have a substantially uniform thickness of approximately15,000 Angstroms.

A contact pattern 108 is then etched in the resist material layer 106and the silicon oxide layer 104 using conventional masking, exposing,etching, and photoresist stripping techniques, as shown in FIG. 3. Thecontact pattern 108 may be defined from the resist material layer 106and silicon oxide layer 104, for example, as a generally rectangularblock as shown in FIG. 4(a), or as a substantially circular block asshown in FIG. 4(b). The contact pattern 108 is preferably formed using aconventional contact hole mask, resulting in the substantially circularblock shown in FIG. 4(b). The minimum lateral dimension of the contactpattern 108 preferably will be approximately 0.4 μm. The contact pattern108 (see FIG. 3) includes a generally horizontal bottom surface 110common to the conductive material layer 102, and generally vertical sidewalls 112 at its outer periphery.

After the contact pattern 108 has been patterned in the silicon oxidelayer 104, the resist material layer 106 is then removed usingconventional stripping techniques, as shown in FIG. 5. Thus, the siliconoxide layer 104 remains as the contact pattern 108. The silicon oxidelayer 104 contact pattern is used as a masking layer when the conductivematerial layer 102 is subsequently etched.

The portion of the conductive material layer 102 not covered by siliconoxide layer pattern 104 is etched using wet etch or dry plasma etchingtechniques. The portions of conductive material layer 102 beneathsilicon oxide pattern 104 being undercut to form a frusto-conical shapedtip or protrusion 114 above the remaining exposed surface of theconductive material layer 102, as shown in FIG. 6. The frusto-conicaltip 114 preferably has a minimum frustum lateral dimension D ofapproximately 0.1 μm. The base of the tip 114 preferably will have abase minimum lateral dimension of approximately 0.4 μm, i.e., the samedimension as the lateral dimension of the contact pattern 108. The tip114 will preferably have a height of approximately 2000 Angstroms. Theremoval of the silicon oxide layer pattern 104 is accomplished usingconventional wet etch techniques, as shown in FIG. 7. The contactpattern 108 thus provides a means for defining the area of contact ofthe base of the frusto-conical tip 114 of the conductive material layer102 of about 0.00785 μm² [π×(0.05 μm)² ]. Although the above dimensionsare given as "preferred", it is understood that goal of the presentinvention is form the tip 114 as small as possible while maintaininguniformity and dimensional control.

A layer of insulative material 116 is deposited onto the conductivematerial layer 102, including the tip 114, using conventional thin filmdeposition methods such as, for example, CVD, to isolate the conductivematerial layer 102, including the tip 114, as illustrated in FIG. 8. Theinsulative material layer 116 may have a substantially uniform thicknessof approximately 2000 to 5000 Angstroms, and preferably will have asubstantially uniform thickness of approximately 2000 Angstroms, i.e.,the same thickness as the height of the tip 114. The insulative materiallayer 116 may comprise silicon oxide or silicon nitride, and preferablywill comprise silicon oxide.

The insulative material layer 116 is then preferably planarized using aconventional abrasive technique such as a chemical mechanicalplanarization (CMP) process, as illustrated in FIG. 9, to form anintermediate structure 160. The CMP process is performed to expose a topsurface 118 of the tip 114 formed on the conductive material layer 102that may also be referred to as the lower electrode.

The chalcogenide memory cell is then formed by incorporating the tip 114of the conductive material layer 102 using conventional semiconductorprocessing techniques such as, for example, thin-film deposition,masking, and etching processes. As shown in FIG. 15, the chalcogenidememory cell preferably includes a base layer of chalcogenide material120, an interlayer dielectric (ILD) layer 124, an optional conductivebarrier layer 128, a second layer of conductive material 122 serving asan upper electrode, and an upper conductive grid interconnect 126.

The chalcogenide material layer 120 may be deposited using conventionalthin film deposition methods, as shown in FIG. 10. The chalcogenidematerial layer 120 preferably is approximately 500 Angstroms thick.Typical chalcogenide compositions for these memory cells are alloys oftellurium (Te), germanium (Ge), and antimony (Sb). Such alloys includeaverage concentrations of Te in the amorphous state well below 70%,typically below about 60% and ranging in general from as low as about23% up to about 56% Te, and most preferably to about 48% to 56% Te;concentrations of Ge typically above about 15% and preferably range froma low of about 17% to about 44% on average, and remain generally below50% Ge, with the remainder of the principal constituent elements in thisclass being Sb. The percentages are atomic percentages which total 100%of the atoms of the constituent elements. In a particularly preferredembodiment, the chalcogenide compositions for these memory cellscomprise a Te concentration of 56%, a Ge concentration of 22%, and an Sbconcentration of 22%. The materials are typically characterized asTe_(a) Ge_(b) Sb₁₀₀₋(a+b), where a is equal to or less than about 70%and preferably between about 40% and about 60%, b is above about 15% andless than 50%, and preferably between about 17% and 44%, and theremainder is Sb.

An optional conductive barrier layer 128 may be provided over thechalcogenide material layer 120 using conventional thin film depositiontechniques, as shown in FIG. 11. The second conductive material layer122 is deposited over the optional conductive barrier layer 128 usingconventional deposition techniques, as further shown in FIG. 11. Theoptional conductive barrier layer 128 is disposed between thechalcogenide material layer 120 and the second conductive material layer122 when these layers are made of such materials which will diffuse intoone another. The optional conductive barrier layer 128 prevents suchdiffusion. Although carbon is a preferred material to form the optionalbarrier layer 128, numerous conductive materials and metals known in theart may be used.

The second conductive material layer 122 provides an upper electrode forthe chalcogenide memory cell. The second conductive material layer 122is preferably titanium nitride (TiN), but may comprise TiN or carbon,and has a thickness of approximately 500 Angstroms. Layers 120,122, and128 are subsequently etched using conventional masking and etchingtechniques, as shown in FIG. 12.

As shown in FIG. 13, the ILD layer 124 is then applied usingconventional thin film deposition techniques. The ILD layer 124preferably is approximately 3500 Angstroms thick, and comprises siliconoxide. The ILD layer 124 is then selectively etched, as shown in FIG.14, using conventional masking and etching processes, to provide accessto the surface of the second conductive material layer 122 defining theupper electrode by an upper conductive grid interconnect 126. The upperconductive grid interconnect 126 may be formed by first applying ablanket deposition of conductive material using conventional thin filmdeposition processes and then by etching the conductive material to formthe upper conductive grid interconnect 126 extending above the surfaceof the ILD layer 124, as shown in FIG. 15. The upper conductive gridinterconnect 126 material may comprise materials such as, for example,Ti, TiN, or aluminum, and preferably will comprise aluminum.

In an alternative embodiment shown in FIGS. 16-21, an intermediatestructure 160 is fabricated by substantially the same method asdescribed above and illustrated in FIGS. 1-9. Elements common to bothFIGS. 1-15 and FIGS. 16-21 retain the same numeric designation. FIG. 16illustrates an intermediate structure (analogous to FIG. 9) afterplanarization of the layer of the insulative material 116 using aconventional CMP process. As shown in FIG. 17, an etch mask 162 isapplied over the insulative material layer 116 to expose the top surface118 of the tip 114. The tip 114 is then etched to form a recess 164 ininsulative material layer 116, as shown in FIG. 18. Preferably, therecess 164 is etched without a mask if an appropriate etchant selectivebetween the insulative material layer 116 and the conductive materiallayer 102 of the tip 114 is used, such as wet etching using NH₄ OH/KOHor dry etching using SF₆.

As shown in FIG. 19, the chalcogenide material layer 120 is applied overthe insulative material layer 116 such that a portion is deposited as alayer of chalcogenide material 120 in the recess 164. A secondconductive material layer 122 is deposited over the chalcogenidematerial layer 120 such that a portion extends into recess 164 to formthe second conductive material layer 122 over the chalcogenide materiallayer 120, as shown in FIG. 20. The second conductive material layer 122and chalcogenide material layer 120 over the insulative material layer116 is then removed, preferably by a CMP process, to form a structure asshown in FIG. 21. An upper conductive grid interconnect 126 may then beformed by conventional techniques to contact the second conductivematerial layer 122, such as shown in the FIG. 15.

It is, of course, understood that the chalcogenide material layer 120 onthe upper surface of the insulative material layer 116 can be removed,such as by CMP, prior to depositing the second conductive material layer122. Furthermore, a carbon layer may be interposed between thechalcogenide material layer 120 and the second conductive material layer122.

In a particularly preferred embodiment, the methods described above areutilized to form an array 168 of chalcogenide memory cells 170 that areaddressable by an X-Y grid of upper and lower conductors, i.e.,electrodes, as shown in FIG. 22. In the particularly preferredembodiment, diodes are further provided in series with the chalcogenidememory cells to permit read/write operations from/to individualchalcogenide memory cells 170, as will be recognized by persons ofordinary skill in the art. Thus, the chalcogenide memory cells 170 canbe utilized in a memory chip 172 which interacts with a CPU (centralprocessing unit) 174 within a computer 176, as schematically illustratedin FIG. 23.

It is also understood that if a conductive barrier layer 128 is requiredbetween the chalcogenide material layer 120 and the second conductivematerial layer 122, a structure shown in FIG. 24 may be formed.

The intermediate structure 160 (FIGS. 9 and 16) may also be formed by analternative method shown in FIGS. 25-32. Elements common to both FIGS.1-9 and FIGS. 25-32 retain the same numeric designation. A layer ofconductive material 102 is deposited onto a substrate 100, asillustrated in FIG. 25. A layer of silicon oxide 104 is deposited ontothe substrate 100 and a layer of resist material 106 is applied onto thesilicon oxide layer 104, as illustrated in FIG. 26. A contact pattern108 is then etched in the resist material layer 106 and the siliconoxide layer 104, as shown in FIG. 27.

After the contact pattern 108 has been patterned in the silicon oxidelayer 104, the resist material layer 106 is then removed usingconventional stripping techniques, as shown in FIG. 28. Thus, thesilicon oxide layer 104 remains as the contact pattern 108. The siliconoxide layer 104 contact pattern is used as a masking layer when theconductive material layer 102 is subsequently etched.

The portion of the conductive material layer 102 not covered by siliconoxide layer pattern 104 is etched using wet etch or dry plasma etchingtechniques. The portions of conductive material layer 102 beneathsilicon oxide pattern 104 being undercut to form a sharp tip 180 abovethe remaining exposed surface of the conductive material layer 102, asshown in FIG. 29. The silicon oxide pattern 104 is then removed, asshown in FIG. 30. A layer of insulative material 116 is deposited ontothe conductive material layer 102 to a level above the sharp tip 180, asillustrated in FIG. 31. The insulative material layer 116 is thenpreferably planarized using a conventional abrasive technique such as achemical mechanical planarization (CMP) process, as illustrated in FIG.32, to form the intermediate structure 160. The CMP process is performedto level and expose a top surface 182 of the sharp tip 180 formed on theconductive material layer 102. This method allows for greater control ofa surface area of top surface 182 of the sharp tip 180 by controllingthe depth of the planarization. Once the intermediate structure 160, thechalcogenide memory cell may then be formed using the methods describedabove and shown in FIGS. 10-15 and FIGS. 16-21.

The present invention includes the simultaneous fabrication of aplurality of tips 114 on the lower electrode, i.e., the conductivematerial layer 102, such that a plurality of chalcogenide memory cellscomprising an array may be created. The drawings show only a single tip114 for ease of illustration of the present invention. Furthermore,while a range of materials may be utilized for each layer, theparticular materials selected for each layer must be selected to provideproper selectivity during the various etching processes as will berecognized by persons of ordinary skill in the art.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description, as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

What is claimed is:
 1. A method for forming a memory cell,comprising:providing a first conductive layer on a substrate; forming atleast one raised portion extending upwardly from said first conductivelayer; providing an insulative material on said first conductive layerand over said at least one raised portion extendly upwardly from saidconductive layer; removing a portion of said insulative material atleast over said at least one raised portion extending upwardly from saidfirst conductive layer to expose a top surface of said at least oneraised portion extending upwardly from said first conductive layer;etching said at least one raised portion extending upwardly from saidfirst conductive layer downwardly from said top surface to form a recessin said insulative material; depositing a programmable resistivematerial in said recess; and depositing a second conductive layer insaid recess over said programmable resistive material.
 2. The method ofclaim 1, wherein said programmable resistive material comprises achalcogenide material.
 3. The method of claim 2, wherein saidchalcogenide material is selected from a group consisting of tellurium(Te), germanium (Ge), antimony (Sb), and combinations thereof.
 4. Themethod of claim 3 wherein said chalcogenide material includes tellurium(Te), germanium (Ge), antimony (Sb) in a ratio Te_(a) Ge_(b)Sb₁₀₀₋(a+b), where a, b, and (100-(a+b)) are in atomic percentages whichtotal 100% of constituent elements, a ≦70% and 15%≦b≦50%.
 5. The methodof claim 4, wherein 40%≦a≦60% and 17%≦b≦44%.
 6. The method of claim 1,wherein said forming said at least one raised portion extending upwardlyfrom said first conductive layer comprises:forming a layer of oxide onsaid first conductive layer; patterning said oxide layer to form spacedoxide elements; and etching said first conductive layer to form said atleast one raised portion extending upwardly from said first conductivelayer below each of said spaced oxide elements.
 7. The method of claim1, wherein said removing said portion of said insulative material atleast over said at least one raised portion extending upwardly from saidconductive layer to expose said top surface of said at least one raisedportion extending upwardly from said first conductive layer comprisesplanarizing said insulative material.
 8. The method of claim 1, whereinsaid removing said portion of said insulative material at least oversaid at least one raised portion extending upwardly from said firstconductive layer to expose said top surface of said at least one raisedportion extending upwardly from said first conductive layer comprisesplanarizing said insulative material and an upper portion of said atleast one raised portion extending upwardly from said first conductivelayer.
 9. The method of claim 1, wherein said depositing saidprogrammable resistive material further comprises isolating saidprogrammable resistive material within said recess.